I found this http://www.faqs.org/childhood/So-Th/Teenagers.html http://www.faqs.org/childhood/So-Th/Teenagers.html that claims that schooling past the age of 14

I found this http://www.faqs.org/childhood/So-Th/Teenagers.html http://www.faqs.org/childhood/So-Th/Teenagers.html that claims that schooling past the age of 14 went from rare to normal between 1901 and 1940.